Distillation of 2-acetoxy-butanal from wood distillate



Oct. 7, 1947. A. A. REITER ET AL I DISTILLATION OF 2-ACETOXf-BUTANAL FROM WOOD DISTILLATE File'd Oct. 30, 1943 2 Sheets-Sheet 2 DIsfI/Iaf/on of Neufra/ized Acef/c Oil. Oil charged f0 .sH/l 36,000 ac. Ref/ax Raf/'0 Approx. 10 f0 1 Pressure 50 mm of Hg Auk Efi @556 25 Fig.3 Aceric Oi/ Dish/lea [X by Volume) 2.5 Fig. 4 Ace/1c 0/1 D/lsfil/ed by Volume) INVENTORS Alfred A. Heifer BY Floyd L. Beman Patented Oct. 7, 1947 UNITED STATES PATENT OFFICE DISTILLATION OF 2-ACETOXY-BUTANAL FROM WOOD DISTILLATE Alfred A. Reiter and Floyd L. Beman,'Marquette, Mich., assignors to Clifls Dow Chemical Company, Marquette, Mich., a corporation of Michigan Application October 30, 1943, Serial No. 508,424

This application is a continuation-in-part of.

traction methods for the recovery of methanol,

acetone, and acetic acid, and residues which, in the older liming'process, usually appeared as tar are separated to a considerable extent into settled tars and a mixture of organic compounds which are soluble in the crude aqueous acetic acid remaining after the pyroligneous acid is settled and demethanolized, and which may be steam-distilled from the aqueous solution along with the acetic acid. Such mixture of dissolved organic compounds usually appears as a non-tarry organic liquid after removal of the water and a major portion of the lower aliphatic acids from the distillate obtained by exhaustive steam-distillation of demethanolized and settled pyroligneous acid, and is herein designated as acetic oil to distinguish it from other portions of tars or oils appearing in the process. In one typical process, the acetic oil is obtained by steam-distilling the settled and, demethanolized pyroligneous acid without prior chemical treatment, extracting the aqueous distillate with an organic solvent, such as ethyl acetate, butyl acetate, ether,

mixtures of ethyl acetate with isopropyl ether,

etc., recovering the solvent by distilling it from the extract at atmospheric pressure, and fractionally distilling the remaining portion of the extract under reduced pressure to recover crude acetic acid and leave the acetic oil as a still residue. Acetic oil so obtained corresponds closely with the still residue remaining when the crude acid of United States Patent 2,19 ,069 is fractionally distilled under reduced pressure to recover therefrom a major proportion of the acetic acid. Acetic oil amounts to a substantial portion of the total organic products obtained from pyroligneous acid produced in the destructive distillation of hardwoods, such as beech, maple, birch, and oak.

Although the character of the acetic oil obtained as described above may vary somewhat, depending upon the exact manner of carrying 6 Claims. (Cl. 202l40) out the several operations of the process, it is usually obtained as a substantially anhydrous, non-viscous, acidic liquid which is at least partially soluble in water or dilute acetic acid and which is miscible with most organic solvents. The specific gravity of the acetic oil is usually greater than 1.0.

Attempts to recover valuable components from the acetic oil by conventional methods involving treatment with alkalies or acids or distillation at atmospheric pressure lead to excessive decomposition.

high reflux ratio, is not feasible because the gradual and substantially constant rise of the distilling temperature and the variations in composition mentioned above make itimpossible to select accurately a fraction rich in a single compo nent. Little, if any, information as to the composition of this oil has heretofore been available other than that it contains phenolic substances, and that small amounts of volatile acids, e. g. acetic and propionic acids, may be recovered from it by steam-distillation. The principal use for,

acetic oil has heretofore been as fuel.

We have discovered. that a hitherto undescribed compound, 2-acetoxy-butanal, is one of the components of acetic oil and that it may be isolated readily in the manner herein described. Other components of the acetic oil, as disclosed in the copending application Just referred to, include in addition to acetic and propionic acids, butyric acid, crotonic acid, acetol, acetol acetate, guaiacol, creosol, and minor amounts of phenol.

The '2-acetoxy-butanal is a colorless mobile liquid with a characteristic odor. It boils at 106 C. under a pressure of 50 millimeters of mercury and at 186 C. under a pressure of 744 millimeters of mercury. It has a specific gravity of 1.035 at 25/25 0., a refractive index of 1.422212 at 25 C., and a freezing point of 0.5 C. Upon saponiflcatlon, it yields acetic acid and an alcohol boiling at 48.5 C. under a pressure of 13 millimeters of mercury and having a freezing point of -32.5 C. The alcoholreduces Fehlings solution in the cold and yields a red coloration with.

Schiiis reagent. It forms a paranitrophenylhydrazone melting at 167.5 to 168 C. and a paranitrophenylosazone melting at 267 C. Upon hydrogenation of the 2-acetoxy-butanal over a Raney nickel catalyst at C. and saponification of the hydrogenated product, butanediol- 1.2 is obtained having aboiling point of 193 C. under a pressure of 745 millimeters of mercury and a Fractional distillation under reduced pressure by the ordinary procedures, even with a from" which the above-mentioned derivatives thereof may be prepared.

Attempts to, collect fractions sufliciently rich in 2-acetoxy-butana1 to permit isolation of the product in a substantially pure state by fractionally distilling the acetic oil-under reduced pressure and selecting the fraction in the usual manner have been uniformly unsuccessful. The difilculty of controlling the fractionationv by observing the distilling temperatures is illustrated in Figure 1 of the drawing, inwhich the vapor temperature of the material distilling in the neighborhood of 106 C. under a pressure of 50 millimeters of mercury, i. e. in the neighborhood of the boiling point of acetoxy-butanal at 50 millimeters pressure, noted periodically during a distillation of a representative sample of acetic oil, are plotted against the. per cent by weight of the acetic oil distilled.

We have found, however, that when the specific gravity of'the material distilling in the neighborhood of 106 C. under a pressure of 50 millimeters of mercury is continuously determined, it

4 necessarily, include the boili g temperature at the distillation pressure of pure 2-acetoxy-butanal. The 2-acetoxy-butanal fraction is then neutralized, i. e. treated with sufilcient alkali to form the metal salts of any free acids which may have distilled with the 2-acetoxy-butana1 from I the acetic oil.

Alternatively,v the acetic oil may be first neutralized and then fractionally distilled, the 2- acetoxy-butanal fraction being collected in the manner previously described. In this case neutralization of the 2-acetoxy-butanal fraction collected is not ordinarilynecessary. The distilling temperature and the specific gravity of the material distilling in the neighborhood of 106 C. under a pressure of 50 millimeters of mercury noted continuously during the distillation of a representative sample of neutralized acetic oil, are shown.in Figures 3 and 4, respectively, of the drawing, plotted against the per cent by volume of material distilled. Figure 3 illustrates the gradual rise in the distilling temperature during varies in such a manner that it passes through a region wherein its average rate of change with respect to the amount of material distilled is relatively small, and, furthermore, that the materail distilling while the specific gravity is passing through this region is rich in 2-acetoxy-butanal. The graph in Figure2 of the drawing was obtained by fractionally distilling a sample of acetic oil and plotting the specific gravity of the material distilling during the distillation against, the

per cent by weight of acetic oil distilled. The region in which the rate of change of the specific.

gravity with respect to the amount of material distilled is relatively small is represented by the portion of the graph near the minimum point. The rate of change of the specific gravity actually reached the value of zero when the gravity was 1.0531. It is thus possible to select a fraction of acetic oil rich cient fractionating column, and beginning collection of the fraction, which distills in the neighborhood of 106 C. when under a pressure of 50 to the amount ofmaterial distilled becomes relatively small; and terminating the collection of the traction when the specific gravity has passed through and is receding from said region. The

distillation may be carried out at any desired pressure, but it is usually carried out under subatmospheric pressure and preferably belowg400 specific in 2-acetoxy-butanalby fractionally distilling the oil through an effi millimeters of mercury since some decomposition of the less heat-stable components of the oil may occur at higher temperatures. Although the collection of the fraction is controlled by means of specific gravity determinations, it is advantageous to observe the distilling temperature during the collection of the fraction, since at agiven pressure the general temperature range in which the fraction distills will ordinarily include or lie close to, e. g. within about 15 0., of the boiling point of 2-acetoxy-butanal at the corresponding pressure, and will thus serve to differentiate it from other fractions of the acetic oil which may be collected over the same range of specific gravity but over different temperature ranges. The range of distilling temperatures observed during the collection of the fraction may, but does not Neutralization of the acetic oil or of the 2-' acetoxy-butanal fraction obtained by distilling the acetic oil is usually accomplished ,by adding an amount of an alkali such as sodium carbonate, potassium carbonate, sodium hydroxide, sodium bicarbonate, calcium hydroxide, etc., suificient to give the mixture a pH of from about 5.5 to about 8. An excess of alkali over that suflicient to com- A bine with any free acids present isusually avoided, since such excess of alkali will tend to cause bydrolysis of the 2-acetoxy-butanal. Neutraliza- 7 tion is usually carried out at temperatures below C. and preferably below 40 C. to reduce hydrolysis of the'Z-acetoxy-butanal to a minimum. Sufflcient water may be used to dissolve the salts formed, alt ough an excess is preferably avoided since 2-ace oxy-butanal is soluble in ,water and isi mo're easily'separated from the aqueous portion of the neutralized mixture if theconcentration 'of salts in the aqueous portion is kept as high as possible. After neutralization is complete, the neutral components of the mixture, which usually form a distinct layer, are separated from the solution of the salts formed during the neutralization, eithermechanically or by extracting with a. water-immiscible organic solvent, e. g. r

with carbon tetrachloride,.ethyl acetate, benzene, ether, etc., and subsequently distilling the extract to recover the solvent. Water-soluble compounds,

such as sodium chloride, may be added to the-- neutralized mixture. to facilitate the separation of the Z-acetoxy-butanal, although this is not usually desirable when acids are to be recovered;

from the aqueous portion of the mixture. Alter natively, a substantially dry alkaline material,

such as powdered sodium carbonatqmay be-used to neutralize the acids present in the 2-acetoxybutanar fraction and the neutral oils may be-separated from the solid salt*"so formed bydecanting or filtering. if

The salts formed'during the neutralization may be treated in any suitable manner to recover the butanal at the distillation pressure.

invention:

acidic compounds originally present in the acetic oil, preferably by acidifying with mineral acids to liberate the organic acids and subsequently separating and fractionally distilling the crude acids so obtained. Crotonic acid may be recovered in this manner from the salts formed during neutralization of the 2-acetoxy-butana1 fraction obfurther purified, e. g. by refractionating. In the case of neutral 2-acetoxy-butanal fractions obtained by first fractionally distilling the acetic oil and then neutralizing the 2-acetoxy-butanal fraction, reiractionation is preferably preceded by a simple distillation to free the material from the lasttraces of salts, since prolonged heating of the 2-acetoxy-butanal with such s'alts may cause considerable decomposition or other byproduct formation. acetoxy-butanal fraction .is usually carried out 'under reduced pressure, and the 2-acetoxy- Refractionation of the 2- butanalcollected when the boiling point of the material distilling is near that of pure Z-acetoxy- Certain advantages of the invention will be seen from the following examples, which are illustrative and are not to be construed as limiting the Escample 1 1360 pounds of unneutralized acetic. oil were -distilled under a, pressure of a little more than 50 millimeters of mercury through an efilcient fractionating column while maintaining a reflux ratio of about B'to' 1. The specific gravity at C. and the temperature of the vapor in, the still head were noted from time to time. The distilling temperature rose gradually without remaining constant at any point for an appreciable time. The rate of change 01' the specific gravity of the material distilling with'respect to the weight 01 a material distilled varied in a substantially regular manner through a series of regions in which its value was successively relatively small and relatively large. When the vapor temperature had reached 108 C. and the specific gravity of the material distilling was 1.046 and decreasing the collection of a fraction rich in Z-acetoxy-butanal .was begun. The collection of the fraction was continued until the specific gravity, after having decreased to 1.031, had increased to 1.058 at which point the collection of the fraction was terminated. The fraction. weighed 108.4 pounds.

Several fractions rich in 2-acetoxy-butanal'collected in the manner just described were combinedand 1680 pounds of the mixture was v neutralized to a pH of about 7 with 145 pounds of sodium carbonate and 810 pounds of water. The neutralized mixture separated into two layers upon standing. The oily layer which weighed 1286 pounds was distilled without fractionation under a pressure of 20 millimeters of mercury to free it from traces of salts and the distillate which weighed 1181 pounds was then redistilled under a pressure of a little over millimetersv of mercury through an eflicient fractionating column while maintaining a reflux ratio of about 8 to 1. The fraction boiling between 107 and 11-5 C. was collected. The fraction collected weighed 6 I 655 pounds and was more than per centpure 2-acetoxy-butanal.

' Example 2 36,000 c. c. of acetic oil was mixed with 36,000 0. c. of water and neutralized to a pH of 7 with 2880 grams of powdered sodium carbonate while maintaining the temperature of the mixture below 40 C. 26,500 c. c. of an oily layer was separated from the mixture and distilled under vacuum without fractionation. The distillate was then distilled under a pressure of 50 millimeters of mercury through an efiicient fractionating column while maintaining a reflux ratio of about 10 to 1. The specific gravity at 25 C. of the material distilling and the distilling temperature were noted periodically. A fore-fraction of 10,800 0. c. was collected. At this point, the specific gravity of the material distilling was 1.050 and decreasing and the distilling temperaturewas 103 C. Collection of a fraction rich in Z-acet'oxy-butanal was then begun. Distillation was continued until the specific gravity after decreasing to 1.035 had increased to 1.065. At this point the collection of the fractionwas discontinued. The fractionso collected consisted of 2000 c. c. of a liquid rich in 2-acetoxy-butanal which was refractionated as in Example 1 and-which yieldeda major proportion of 2-acetoxy-butanal of high purity.

Other modes of applying the principle of the invention may be employed instead of those'explained, change being made as regards the method herein disclosed, provided the step' or steps stated by any of the following claims or the equivalent of such stated step or steps be ployed.

We, therefore, particularly point out and distinctly claim as our invention: 1

1. In a method for separating 2-acetoxybutanal from a mixture selected from the class consisting of acetic oil and acetic oil which has been freed of acidic ingredients lby neutralization,

the steps which include: fractionally distilling the mixture and beginning collection of a fraction of distillate, which boils in the neighborhoodgot the boiling point of 2-acetoxy-butanal at the distillation pressure, when the specific gravity of the material distilling is decreasing and is ap-' preaching a region wherein its average rate 01 change with respect to the amount of material distilled is relatively small, .and terminating collection of the fraction when the specific gravity has passed through and is receding from said region.

2. In a method for separating 2-acetoxybutanal from acetic oil, the steps which include: fractionally distilling the acetic oil and beginning collection of a fraction of distillate, which boils in the neighborhood of the boiling point of 2- acetoxy-butanal at the distillation pressure, when the specific gravity of the material distilling is decreasing and is approaching a region wherein its average rate of change with respect to the amount of material distilled is relatively small, and terminating collection of the fraction when the specific gravity has passed through and is receding from said region.

3. In a method for separating 2-acetoxy-buborhood of the boiling point of 2-acetoxy-butanal at the distillation pressure, when the specific gravity of the material distilling is decreasing and is approaching a region wherein its average rate of change with respect to the amount of material distilled is relatively small, and termi-- nating the collection of the fraction when the specific gravity-has passed-through and is receding fromlsaid region; neutralizing the collected traction to a pH of from about 5.5 .to about 8 at a temperature below 80 C.; separating the neutral organic components from the neutralized mixture; fractionally distilling said neutral organic components under reduced pressure and collecting a fraction of distillate consisting substantially of pure 2-acetoxy-butanal.

5. In a method for separating 2-acetoxy-bu- I tanal from acetic oil, the steps which include: freeing the acetic oil from acidic ingredientsby neutralization at a temperature below 40 C. and to a pH value between 5.5 and 8; subsequently fractionally distilling the neutralized acetic oil and beginning collection of a fraction of distillate, which boils in the neighborhood of the boiling point of 2-acetoxy-butanal at the distillation pressure, when the specific gravity of the material distilling is decreasing and is vapproaching a regionwherein its average rate of change with respect. to the amount of material distilled is relatively small, andterminating collection of the fraction when the specific gravity has passed through and is receding from said region.

6. In a method for separating 2-acetoxy-butanal from acetic oil, the steps which'include: iractionally distilling the acetic oil and beginning collection of a fraction of distillate, which boils in the neighborhood of the boiling point of 2- acetoxy-butanal at the distillation pressure, when the specific gravity of the material distilling is decreasing and is approaching a region wherein its average rate of change with respect to the amount of material distilled is relatively small, terminating collection of the fraction when the 4 specific gravity has passed through and is reced- 10' ing from said region; and subsequently freeing the collected fractionfrom acidic ingredients by neutralizing the same at a temperature below 40 C. and to a pH value between 5.5 and 8.

ALFRED A. REITER. FLOYD L. BEMAN.

REFERENCES CITED The following references are of record in the flle of this patent:

UNITED STATES PATENTS Number Name Date 1,868,102 Henderson et a1. July 12, 1932 2,251,771 Wynn et al Aug. 5, 1941 2,256,149 Long Sept. 16, 1941 2,309,937 Dietrich Feb. 2, 1943 OTHER REFERENCES Shriner and Fuson, The Systematic Identification of Organic Compounds," second edition (1940), published by John Wiley and Sons, Inc. (Copy in Library of Congress, pages 101-105.)

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